In general, an optical coherence tomography (OCT) is one of advanced medical imaging technologies that currently come into the significant spotlight in the market. The optical coherence tomography (OCT) possesses a representative advantage in that it can perform a tomographic imaging of the inner microstructure of a biological tissue with a micro-high definition in a non-invasive and high-speed manner. Since an optical coherence tomography (OCT) for ophthalmic use for imaging of a retina was greatly successful in commercialization, the speed of the research has been accelerated on commercialization of various OCT-related products including an OCT for endoscopy, an OST for skin diagnosis, an OST for tumor diagnosis, and so forth around the world. In addition, researches are overly actively in progress on technologies for allowing the image acquiring speed to be made fast, acquiring high resolution images, reducing the manufacturing cost, minimizing the influence of noises, and so forth.
FIG. 1 is a basic schematic view illustrating a spectral domain optical coherence tomography (SD-OCT) system according to the prior art. A light source 21 employs a low-coherence broadband light source. For example, light source 21 employs a light source having a wavelength with a bandwidth of 800 nm and 1300 nm in the OCT for ophthalmic use. Light generated from the light source 21 is distributed to a reference arm where a mirror 22 is positioned and a sampled arm where an object to be examined is positioned while passing through an optical distributor 24. When the travel distance of light from the optical distributor 24 to the mirror of the reference arm is equal to the travel distance of light from the optical distributor 24 to the object to be examined of the sample arm, the light reflected from the mirror and the light reflected from the sample meet each other to generate an interference signal. The produced interference signal is incident on a spectrometer 26 and then is finally detected by a line scan camera via a diffraction grating and a lens.
A conventional OCT system for ophthalmic use is constructed as the above-mentioned basic system. The OCT system allows parallel light to be incident on an eyeball using two lenses in the sample arm and then to be focused on the retina by a crystalline lens present in the eyeball. There frequently occurs the case where the cornea and the retina are required for evaluation and diagnosis, but an OCT technology has not been proposed yet which can measure the cornea and the retina simultaneously.
That is, in case of the conventional OCT system for ophthalmic use, since the position of the mirror of the reference arm is fixed so that an image is acquired at a portion where a single focal point is formed by the lens of the sample arm, it is impossible to simultaneously measure the cornea and the retina that have different focused areas using a single spectrometer. The reason for this is that when the position of the mirror of the reference arm is set based on the focal formation distance of the retina, acquisition of video information with respect to the cornea is physically impossible due to a significant difference between the light travel distance from the optical distributor to the retina the light travel distance from the optical distributor to the cornea.
Further, the cornea is positioned in front of the crystalline lens in the eyeball, and the retina is positioned at the rear of the crystalline lens in the eyeball, so that when the parallel light is transmitted to the retina to acquire an image of the retina, a focus is not formed at the cornea, which makes it impossible to acquire an image of the cornea. Thus, an existing OCT system entails a problem in that it is designed for measurement of either the retina or the cornea, and two spectrometers are needed to solve this, leading to an increase in the number of the spectrometers, and thus a sharp increase in the manufacturing cost. This makes it difficult to achieve a compact structure of the OCT system.